The present invention is directed to a wiring harness for a heating, ventilating and air conditioning (HVAC) system and, more particularly, to a method and apparatus for accurately and automatically, configuring the controller of the HVAC system to recognize the system configuration.
Large scale HVAC systems are tailored to the owner's specific needs and requirements. An HVAC system will typically include one or more compressors, one or more condensers, one or more evaporators, and one or more condenser fans, all of which are controlled by a controller. The HVAC system can also include an economizer, a heat pump, a building automation system, and a heating system. The controller is generally provided to monitor and control the operation of the system as configured by the owner of the HVAC system. To function properly, the controller must be accurately programmed to recognize the configuration of the system. If the controller is not capable of being programmed, field service personnel are required to stock multiple versions of the controller, one version for each HVAC system configuration.
Many problems which are found in prior systems result from human error in programming or identifying the initial HVAC system configuration to the controller. This initial configuration problem occurs both in the installation of new systems, and in the repair or upgrading or existing systems.
Prior systems have taken two approaches to solving this problem.
Firstly, prior systems have relied on centralized configuration jumpers and DIP switches to inform the controller of the system's configuration. Configuration jumpers are a series of paired input terminals which are individually connected or disconnected by an installer to inform the controller of the presence or absence of particular system elements or functions. Similarly, a DIP (dual in-line package) switch is a bank of small switches adapted for easy insertion into a printed circuit board. The individual switches of the DIP switch are opened or closed by an installer to provide an input to the controller representative of the presence or absence of particular system functions or elements. However, configuration jumpers and DIP switches are expensive, and require the design of the controller to include a centralized, external location. This centralized location is costly both in terms of design and in terms of material. Also, both configuration jumpers and DIP switches are subject to installer error during the initial system configuration, and both are subject to accidental alternation once the system has been established. Additionally, DIP switches have been known to be install backwards, leading to additional errors.
For example, U.S. Pat. No. 4,545,210 to Lord shows an electronic program control including programmable headers with fixed jumpers which develop to binary code to configure a microprocessor to the physical characteristics of an assembled refrigeration unit. The programmable header is programmed at the factory by selectively breaking the jumpers to develop the binary code. Programming of the microprocessor for accessory equipment is performed by field service personnel using small dip switches to develop a binary code for the microprocessor. Both the dip switches and the selectively broken jumpers of the programmable header are subject to considerably human error in determining the physical characteristics of the assembled refrigeration unit and the accessory equipment. Additionally, programmable headers require considerable design effort in laying out the configuration of the controller, to ensure that there exists a single location containing all of the connections to the programmable header, and all of the connections to the dip switches. Furthermore in addition to the cost and limitations of such a design effort, the cost of the programmable headers, the fixed jumpers, the connections, and the dip switches can add considerable expense to a controller.
Secondly, some prior systems take the approach of modifying a standard wiring harness during assembly to match the requirements of the desired systems. In this approach, wires and connectors are added or removed as necessary during assembly of the controller and the HVAC system. Such an approach is costly in terms of material, is labor intensive, and is very subject to human error. Additionally, such an approach may require considerable rewiring if the controller is replaced or upgraded.